Grease compositions are widely used for lubricating bearings and other structural components. A grease is an essential product to reduce, for example, wear, friction, running temperatures and energy losses.
Greases are materials which comprise a base oil that is thickened with a metal soap, and they are usually prepared by reacting a metal hydroxide with a fatty acid in the presence of the base oil. Conventional metal soap greases require an energy intensive grease cooking and milling process in order to achieve proper thermal mechanical stability. Conventional metal soap greases can still be sensitive to poor thermal mechanical stability and can require additional treatments. It is known to improve further the stability, and thus the lubricating capacity, of conventional greases by adding solid additives during the thickening process. Examples of such solid additives are, for example, molybdenum disulfide, graphite, zinc oxide and/or a silica gel. The process of grease cooking and milling and additional treatments is relatively expensive because it is carried out at an elevated temperature over a relatively long period of time. Moreover, the greases so prepared are still unsuitable for a variety of applications, and not all conventional greases are suitable for food and beverage processing applications because they contain considerable amounts of metal hydroxides. In this respect reference is for instance made to U.S. Pat. No. 2,514,331 in which a lime soap grease is prepared by cooking lime and an animal fat at an elevated temperature. The lime soap grease thus prepared typically needs an excess amount of lime to completely neutralize the large variety of fatty acids that are present in the grease. Moreover, it is noted that the performance of such lime soap greases leaves much room for improvement. A soap grease is also known from US 2003/0087768 which comprises a base oil, a thickener comprising a complex lithium soap, and an agent for reducing the coefficient of friction which comprises hydrophobic silica. The soap grease so prepared also contains a considerable amount of metal hydroxide, whereas the grease lubricating properties leave considerable room for improvement.
Consequently, there is a need for greases which can easily be manufactured at low costs (i.e. low temperatures), which are stable and show highly attractive lubricating properties. In addition, there is a need for greases that are biodegradable, environmentally friendly and food compatible.